1. Field of the Invention
This invention relates generally to a metal-bonded tool and a method of manufacturing same, and more particularly to a metal-bonded tool which uses an iron-base alloy as a bond to which abrasive grains are bonded.
2. Description of the Prior Art
Metal-bonded diamond tools which use diamond as abrasive grains have been available for grinding or finishing a variety of ceramics such as alumina, aluminum nitride, and silicon nitride. Also, metal-bonded boron nitride tools whose abrasive grains are cubic boron nitride (CBN), are considered to be effective for grinding or finishing hard metals. In metal-bonded diamond tools which use diamond powder as abrasive grains, the bonding strength of their bonds and abrasive grains are provided by sintering after mixing metallic powder or metallic powder containing metallic compounds and abrasive made of diamond powder.
In the case of metal-bonded diamond tools suitable for high efficiency grinding, the powder is made by pulverizing the chips of iron-base casting containing carbon in a ball mill or by stamping. In the powder made by these methods, the sizes of the carbon or graphite precipitates is large, e.g. from dozens to 100 .mu.m, and the shapes are uneven. Therefore, carbon or graphite precipitates in the powder are apt to dropout during pulverization, and carbon in the powder becomes uneven. The diameter of carbon or graphite precipitates of tool materials is larger. Therefore, the loss of carbon or graphite precipitates creates hollows, and grinding or finishing chips accumulate in the hollows. This causes the destruction or the plastic deformation of bond by galling. These are the causes of lower grinding efficiency or finishing accuracy.
In processes of manufacturing diamond tools, carbon or graphite powder has been added to disperse in the sinter. However, the above problems could not be solved, because it was difficult to disperse very small carbon grains evenly into the material.
As stated above, the conventional tools experience a loss of carbon or graphite precipitates, leading to the loss of abrasive grains, and this causes lower grinding efficiency or finishing accuracy.